In platen presses heatable press platens are commonly used. The platen press can be a cycle press or a continuous press. The fluid medium can be for instance steam, water or oil. Depending on the conditions which prevail during the production of chip board, fiber board, laminated board and the like, the fluid medium can also cause cooling.
Collecting channels define those channels which supply the fluid medium to the heating channels or evacuate the fluid medium therefrom.
The return channels define those connecting a plurality of heating channels, for instance in a meander-like manner, with the aid of inserted deflecting elements. In practice a great variety of flow patterns can be created. Sometimes, depending on the thickness of the platen, the channels are arranged on several levels.
In the generically known process as currently practiced, the heating channels are drilled first, and after the return channels or the collecting channels are traced, for instance by arranging particular components, the deflection elements are also inserted and are set against the steel platen. This is cumbersome.
However, it is also known to make bores in the steel plates already provided with heating channels, which will constitute the return or collecting channels. This creates difficulties, because the drills for the collecting channels or return channels are easily destroyed and/or deflected, as a result of their passage through the already open heating channels. In fact, in the modern fabrication, in order to obtain such bores, it is necessary to work with deep-hole drilling tools and corresponding drilling machines, whereby the drillings have to be removed from the cutting zone with considerable amounts of a lubrication medium.
When, during the boring of a collecting or return channel, the drill passes through an already-drilled heating channel, the lubrication medium can be discharged and the drill can have a dry run until it is destroyed and/or can be deflected. The circumstances are similar when the collecting or return channels are drilled first. Besides, it requires extraordinary efforts to insert the deflecting elements in the return channels made by this method.